Sorry for digging this very late. But as part of integrating dma_map v7 
& sysmmu v12 on 3.3-rc5, I am facing below issue:

a) By un-selecting IOMMU in menu config, I am able to allocate memory in 
vb2-dma-contig

b) When I enable SYSMMU support for the IP's, I am receiving below fault:

Unhandled fault: external abort on non-linefetch (0x818) at 0xb6f55000

I think this has something to do with the access to the SYSMMU registers 
for writing the page table. Has anyone of you faced this issue while 
testing these(dma_map+iommu) patches on kernel mentioned above? This 
must be something related to recent changes, as I didn't have issues 
with these patches on 3.2 kernel.

Regards,
Subash


On 03/02/2012 01:35 PM, KyongHo Cho wrote:

On Thu, Mar 1, 2012 at 12:04 AM, Marek Szyprowski
[off-list ref]  wrote:

quoted

+/**
+ * arm_iommu_map_sg - map a set of SG buffers for streaming mode DMA
+ * @dev: valid struct device pointer
+ * @sg: list of buffers
+ * @nents: number of buffers to map
+ * @dir: DMA transfer direction
+ *
+ * Map a set of buffers described by scatterlist in streaming mode for DMA.
+ * The scatter gather list elements are merged together (if possible) and
+ * tagged with the appropriate dma address and length. They are obtained via
+ * sg_dma_{address,length}.
+ */
+int arm_iommu_map_sg(struct device *dev, struct scatterlist *sg, int nents,
+                    enum dma_data_direction dir, struct dma_attrs *attrs)
+{
+       struct scatterlist *s = sg, *dma = sg, *start = sg;
+       int i, count = 0;
+       unsigned int offset = s->offset;
+       unsigned int size = s->offset + s->length;
+       unsigned int max = dma_get_max_seg_size(dev);
+
+       for (i = 1; i<  nents; i++) {
+               s->dma_address = ARM_DMA_ERROR;
+               s->dma_length = 0;
+
+               s = sg_next(s);
+
+               if (s->offset || (size&  ~PAGE_MASK) || size + s->length>  max) {
+                       if (__map_sg_chunk(dev, start, size,&dma->dma_address,
+                           dir)<  0)
+                               goto bad_mapping;
+
+                       dma->dma_address += offset;
+                       dma->dma_length = size - offset;
+
+                       size = offset = s->offset;
+                       start = s;
+                       dma = sg_next(dma);
+                       count += 1;
+               }
+               size += s->length;
+       }
+       if (__map_sg_chunk(dev, start, size,&dma->dma_address, dir)<  0)
+               goto bad_mapping;
+
+       dma->dma_address += offset;
+       dma->dma_length = size - offset;
+
+       return count+1;
+
+bad_mapping:
+       for_each_sg(sg, s, count, i)
+               __iommu_remove_mapping(dev, sg_dma_address(s), sg_dma_len(s));
+       return 0;
+}
+

This looks that the given sg list specifies the list of physical
memory chunks and
the list of IO virtual memory chunks at the same time after calling
arm_dma_map_sg().
It can happen that dma_address and dma_length of a sg entry does not
correspond to
physical memory information of the sg entry.

I think it is beneficial for handling IO virtual memory.

However, I worry about any other problems caused by a single sg entry contains
information from 2 different context.

Regards,

Cho KyongHo.
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